FIG. 5 is a circuit block diagram of in-vehicle power supply device 500 in a vehicle having a conventional idling stop function. FIG. 6 is a timing chart of an output voltage of in-vehicle power supply device 500.
A positive electrode side of secondary battery 1 is connected to input terminal 2a of power supply circuit 2 via fuse 3 while output terminal 2b of power supply circuit 2 is connected to load 4. In power supply circuit 2, boost converter 5, connection-assist diode 6, and switch 7 are arranged in parallel and connected to input terminal 2a and output terminal 2b. The anode of connection-assist diode 6 is connected to input terminal 2a of power supply circuit 2 while the cathode of connection-assist diode 6 is connected to output terminal 2b of power supply circuit 2.
Boost converter 5 of power supply circuit 2 boosts up a voltage of secondary battery 1 when a vehicle restarts from an idling stop state so as to allow the vehicle to restart stably. Switch 7 opens only when boost converter 5 performs a boosting operation. In this operation, control device 8 provided in a vehicle controls boost converter 5 and switch 7. Connection-assist diode 6 is provided in power supply circuit 2 in order to prevent a boosted voltage from being supplied to input terminal 2a during a boosting operation of boost converter 5, and to allow secondary battery 1 to supply electric power to load 4 even when switch 7 is broken to open. That is, as long as either connection-assist diode 6 or switch 7 is in a normal state, secondary battery 1 can supply electric power to load 4.
Power supply circuit 2 judges whether boost converter 5 operates normally or not. It is judged, based on an voltage of output terminal 2b during non-boosting and boosting, whether boost converter 5 in power supply circuit 2 operates normally or not. First, for non-boosting, control device 8 stops an operation of boost converter 5 and closes (turns on) switch 7. In this case, control device 8 detects a voltage of output terminal 2b and stores the value of the detected voltage. By contrast, for boosting, control device 8 instructs boost converter 5 to operate and opens (turns off) switch 7. In this case, control device 8 detects the voltage of output terminal 2b, and stores the value of the detected voltage. After that, control device 8 obtains the difference between the value of the voltage of output terminal 2b during the non-boosting and the value of the voltage of output terminal 2b during the boosting. Control device 8 compares the difference with a predetermined threshold V0, and judges whether boost converter 5 operates normally or not.
An in-vehicle power supply device similar to in-vehicle power supply device 500 is disclosed, for example, in PTL 1.